In hydrocarbon producing wells, in particular, natural gas wells, multiple gas producing formations in the vertical strata of the gas field may be present. A well may pass from multiple formations along its vertical height. When drilling a well that contains multiple formations, it is common practice to place a plug in the well to separate vertically adjacent formations. To protect the plug itself, it is known to place a sufficient amount of sand on top of the plug. A well having sand placed in this manner is referred to an “underbalanced well”. In a well D with multiple formations A, as shown in FIG. 1, plug B is placed in well D to separate each formation A. Sand C is then placed on top of each plug B.
When the uppermost formation has almost been depleted, the plug and the sand separating the uppermost formation and the formation beneath it needs to be removed. To remove the sand, it is known to lower a string of tubing into the well until the lower end of the tubing is near the sand. Coupled on top of the tubing is a valve subassembly, such as a ball valve subassembly commonly known to those skilled in the art. A safety valve subassembly is often used on top of the first valve subassembly. The safety valve subassembly typically incorporates a valve actuator known as an emergency shut-in device or “ESD”. Due to the explosive nature of natural gas, the ESD is operated by a compressed air or hydraulic line as opposed to an electrically-controlled actuator. The ESD is controlled by a remotely located switch situated near the floor of the well service rig so that it is easily accessible by an operator.
When a joint of tubing is lowered into a well, the first valve subassembly is closed. The tubing may be rotated about its longitudinal axis so that it may descend into the well easily. This requires that the control line to the ESD of the safety valve subassembly to be disconnected as the safety valve subassembly will also rotate as the tubing is lowered into the well. Once the tubing is positioned to remove the sand in the well, the control line is reconnected to the ESD and the first valve subassembly is opened thereby allowing the pressure of the formation to force gas up the tubing drawing along sand with it. In the event of an emergency, the ESD can be activated by an operator to close the safety valve subassembly and stop the sand cleanout operation.
If additional joints of tubing are required to be tripped into the tubing string, the first valve subassembly is closed and the control line to the ESD is disconnected. The connection between the first valve subassembly and safety valve subassembly is broken and another joint of tubing is inserted between the first valve subassembly and the safety valve subassembly. The second valve subassembly is also placed between the second joint of pipe and the safety valve subassembly. The second valve subassembly is initially placed in the closed position. The first valve subassembly is then opened and the string of tubing is then lowered further into the well. When the string is in position, the control line is reattached to the ESD and the second valve subassembly is then opened to continue with the sand cleanout operation. If multiple joints of tubing are required, this procedure is repeated for each joint of tubing placed in the tubing string.
As the safety valve subassembly with the ESD is part of the tubing string, the control line must be repeatedly disconnected and reconnected for each joint of tubing added to the tubing string. This procedure adds considerable time and inconvenience to the operation. To avoid this inconvenience, some well service operators may choose not to use a safety valve subassembly with an ESD at all. This causes a potentially hazardous situation for operators as there is no standby emergency shutdown mechanism to shut down the operation in the event of an emergency.
Therefore, it is desirable to have a safety valve subassembly with an ESD that does not have to have its control line disconnected and reconnected every time a joint of tubing is tripped into or out of the tubing string.